In general, injection molding is a process of manufacturing various plastic products by putting and melting usually a raw material of thermoplastic resin in an injection cylinder of an injection molding machine, forcing the molten resin into the cavity of a metal mold with a hydraulic plunger or the screw of an extruder, and cooling and hardening the molten resin therein, in which the metal mold used in the injection molding is called an injection mold.
The injection mold is manufactured to correspond to the size and shape of a product that is injection molded, and replaceably mounted so that various products can be injection molded from the same injection molding machine.
Meanwhile, when the size of a molded product is small, the injection mold disclosed in Korean Patent Registration No. 10-0344901 is used for injection molding.
According to the injection mold disclosed in Korean Patent Registration No. 10-0344901, an upper core and a lower core are disposed between an upper holder block and a lower holder block and an ejector is disposed under the lower holder block.
Accordingly, the molded product formed in the cavity formed by the upper core and the lower core can be separated from the mold by an ejecting pin moving into the cavity, through the lower holder block and the lower core.
However, the related art having the configuration described above has the following problems.
A piezoelectric ceramic product for a piezoelectric polymer composite is molded in a shape between several micrometers (μm) and several millimeters (mm). Further, in order to mold a piezoelectric ceramic product for a piezoelectric polymer composite, one piezoelectric ceramic product can be formed by injecting a material after manufacturing a plastic mold and then melting the plastic mold after molding is finished.
Therefore, in order to mold a plurality of piezoelectric ceramic products, it is required to manufacture plastic molds that are as many as the products. This increases the manufacturing cost and the manufacturing time, which consequently makes mass production difficult.
Further, when the piezoelectric ceramic is molded by a common injection mold, there is a portion with a large aspect ratio for the characteristics of the injection-molded piezoelectric ceramic. The aspect ratio of the ejecting pin for removal is correspondingly increased to mold the portion with a large aspect ratio, so that the ejecting pin has a thin and long shape.
Further, when the injection mold described above is mounted on a large and high-capacity injection molding machine that is generally used, the lower holder block becomes very thick with respect to the size of the upper core and the lower core while molding for a micro-sized shape, so that the length of the ejecting pin passing through the lower holder block is necessarily increased.
In this structure, since the ejecting pin is long and thin, it may be deformed or broken due to the load that is vertically applied, which causes a defect in the product.
In particular, when not only the size of a piezoelectric ceramic product that is injection molded is small, but a complex shape, such as a groove, a slot, and a hole, is to be molded, the ejecting pin becomes necessarily thinner and accurate, so that the problem described above becomes more serious.
Obviously, although it may be possible to produce accurately machined ejecting pin by using a high-strength material in order to remove the problem, the manufacturing cost considerably increases, which is not preferable.